Acetyl-CoA carboxylase carboxyltransferase β subunit enhances NaHCO₃ tolerance and fat content

The widespread global distribution of saline-alkali land poses a major challenge to agricultural production and water resource management. Saline-alkali stress is extremely harmful to the growth of most plants, but green algae can survive in saline-alkali soil. A saline-alkali tolerant (SAT) Chlorella strain that shows strong sodium bicarbonate (NaHCO₃) tolerance was isolated previously. In this study, we cloned the gene (ChaccD) encoding the carboxyltransferase β subunit of acetyl-CoA carboxylase from SAT Chlorella by screening a full-length yeast cDNA library constructed from cells exposed to NaHCO₃. The ChaccD expression level was elevated in response to NaHCO₃ treatment and the ChaccD protein was localized to the chloroplasts. ChaccD-transgenic rice and ChaccD-overexpressing Chlorella showed stronger NaHCO₃ tolerance, and improved crude fat and free fatty acid contents were observed in mature rice grains and Chlorella cells treated with NaHCO₃. These data indicated that ChaccD is a candidate to confer saline-alkali tolerance for cultivation and nutrition of rice in saline-alkali soil. In addition, ChaccD may be involved in the conversion of NaHCO₃ into lipids, which could be relevant to the production of biodiesel feedstocks, though further validation is required.